Device for producing amorphous ceramic products or metal alloys

ABSTRACT

The device disclosed comprises a high-pressure autoclave in which a moulded blank of the sample is heated by means of laser beams to the melting point and then rapidly cooled. The sample is maintained in a processing position (2) in an autoclave (1) without contact by means of an acoustic levitation device (12). Laser beams are directed through windows (19) in the autoclave onto the processing position and heat the sample. The molten sample then passes between two mutually impacting dies (20,21) by which it is crushed and thus rapidly cooled.

The invention relates to a device for producing amorphous ceramicproducts or metal alloys by means of a high pressure autoclave in whichfirstly a preform of the sample is heated by means of laser beams up tomelting temperature and is then rapidly cooled down.

Amorphous metal alloys, also called metal glasses, have been known fortwenty years. They are constituted by a noncristalline body having anunsystematic structure which is obtained by cooling down a moltencharge. The cooling is carried out at high speed (at about 10⁶ Ks⁻¹)down to a temperature at which crystallization is no more possible.

Such amorphous substances show new mechanical, electrical and chemicalcharacteristics which are not achieved by the corresponding crystallizedvariations.

The high cooling speed of the molten material is decisive for theproduction of such amorphous substances. Thus, a method is known inwhich the molten material flows from an inductively heated melting potonto the periphery of a copper disk having a band scraper and rotatingabout a horizontal axis. It is also possible to introduce the moltenmaterial between two narrow copper disks rotating about horizontal axesor to bring it onto the disk surface of a copper disk rotating about itsvertical axis.

It has also previously been proposed to maintain an electricallyconductive molten material without container magnetically in suspensionand to heat it up inductively in such a way that impurities from themelting pot cannot impair the alloy. In space tests, droplets of anon-conductive material without melting pot have also been heated up bymeans of laser beams. The droplets are held in space in a definedposition by means of air nozzles.

From DE-A 20 32 577 a method is known per se for melting fireproofmaterials by means of at least two laser beams directed through windowsin a process autoclave onto a preform, a method which is preferablycarried out under gravity free space condtions.

Apart from the cost which is involved in the transfer of production ofsuch alloys-into space, the problems of sample positioning and samplestability are not yet solved in a satisfactory manner. It is the aim ofthe invention to provide a device for producing amorphous substanceswhich makes it possible to produce such amorphous substances, and evenelectrically non-conducting substances, at high purity within thegravity field of the earth. This aim is reached by the device ascharacterized in claim 1. As to preferred embodiments of the invention,reference ist made to the subclaims.

The invention will now be described by means of a preferred embodimentand the unique drawing which shows schematically and in perspective adevice according to the invention.

The device contains as essential element an autoclave 1 of essentiallycylindrical shape, in the central point of which is located the processposition 2, i.e. the place where a spherical sample is to be heated andcooled. The sample originates from a sphere-feed device 3, which isaxially mounted on the autoclave 1 and which holds at disposal a seriesof spheres or preforms with the composition of the desired alloy oneafter the other in view of the transfer to the process position 2. Tothis end, this device contains a step-by-step motor 4 and anindividualization disk 5 driven by it, as well as a hollow shaft 6,through which a sphere released by a magazine 7 can drop into theprocess position 2. Opposite to the process position of the sphere feeddevice 2 a housing 8 is mounted on the autoclave 1, which housingcontains a recipient 9 for collecting the finished samples as well as alift motor 10 which carries via a spindle 11 an acousticresonance-levitation installation 12. The latter is situated below theprocess position 2 and contains several electrically excitablepiezoceramic disks.

Between the process position 2 and the levitation installation 12 thereis further inserted an acoustically permeable catch basket 26, and abovethe process position there is provided a reflector disk 13, through thecentral hole of which the sphere is fed from the magazine 7. Theacoustic waves generated by the levitation installation are reflected bythe reflector disk 13 at a distance capable of resonance, so that aprecise, driftless, stable, repeatable positioning without oscillationof the sphere is achieved, without polluting the sphere by contact witha wall. This method works at autoclave pressures from 10 Bar to 1000 Barand at temperatures from 1000 K to 4000 K and more as well as with anyinert gases, and enables the contactless support of metallic as well aselectrically non-conducting materials. The sphere diameters can liebetween 0.2 and 2 mm and the levitation time can be extended at wish andonly requires a small amount of power, compared for example withelectromagnetic induction levitation techniques. By adjusting the liftmotor 10, the sphere can be exactly levitated into the process position.

The heating up of a sphere in the process position 2 is carried out bytwo laser beams 14 and 15, which can be derived from a common Nd-YAGgenerator. By a beam divider mirror 16 and 17, the two laser beams arerespectively divided into two respective beams, which are directed viaderivation mirrors 18 and through windows 19 in the wall of theautoclave 1 onto the process position 2, and this in such a way thatfacing beams do not dazzle each other and thus the generators cannot bedestroyed by dazzling light. Preferably, two laser beams respectivelyrun along the edges of two imaginary four-sided pyramids facing eachother, the tops of which are constituted by the process position and theedges of which are mutually aligned. Two laser beams respectivelyattributed to a pyramid lie in one plane, Which is orthogonal to thecorresponding plane of the other laser beams.

Also directed onto the process position, but perpendicular to the axisof the autoclave, two stamps 20 and 21 are movably disposed inalignment, the front faces of which act as cooling heads and lie ateither side of the process position thereby facing each otherdiametrically. The guiding channel for the stamp 20 or 21 respectivelyis tightly mounted in the wall of the autoclave 1 and under thehydrostatical gas pressure of the latter. By simultaneously applying anelectrical pulse on dive coils 22 and 23 acting on the stamps, the twostamps are accelerated in opposite directions and crash with a crashspeed of for example 12.0 msec⁻¹. By this crash, a molten sphere whichis situated in the process position, is crushed between the front facesof the stamps and cooled down with high speed (higher than 10⁶ Ksec⁻¹)and compressed to become a flat cylinder of 10 to 50 μm thickness. Thecooling speed is variable via the acceleration stroke.

In order to be able to precisely follow and possibly influence theprocess, a six-wavelength-pyrometer 24 is provided, which is directedonto the process position through a further window 25 in the autoclavewall and which permits the continuous measurement of temperaturesbetween 1200 and 5000 K. For example, optical wavelengths 500 nm, 600nm, 680 nm, 800 nm, 960 nm and 1040 nm are processed. The apparatus cancarry out a measurement in microseconds and spatially resolve 50 μmconcerning the minimum measure spot size. Such a pyrometer is describedin the journal Temperature, 1982, vol. 5, pages 439 to 446.

An electronic development control (not shown) coordinates the functionof the laser generators, the levitation installation and the coolingstamps as follows:

Firstly, the sphere magazine 7 of the feed device 3 is filled with about50 preforms of the sample and then closed in a gastight manner. Then theautoclave is filled with the gas suited for the process and brought tothe desired pressure. The following step is to bring a preform sphereinto the feed channel 6 by operation of the motor 4, from where it dropsinto the catch basket 26 just below the process position 2. When now thepiezoceramic levitation installation 12 is switched on, the preform inthe process position comes into a suspension state which can possibly beadjusted by means of the lift motor 10. Now, the two lasers 14 and 15are activated for a short time and simultaneously, the pulse durationand the pulse energy depending on the desired temperature. The preformthen melts in a reproducible short time, so that now the dive coils 22and 23 can be activated and the stamps 20 ands 21 can crush the moltensample between them. After the rebounding of the stamps and theswitching off of the levitation installation, the finished sample dropsvia a funnel into the collecting recipient 9 in the lower part of thedevice.

The whole process can be followed via the pyrometer 24.

Thereafter, the second preform can immediately be transferred from themagazine 7 into the process position 2 and be treated in the same way.

It has to be noted that the manufacture of a sample only takes afraction of a second and that as many samples can be manufacturedwithout interruption as the magazine 7 and the collecting recipient 9can contain. By optimization of the lapse of time between heating up andcooling down, the evaporization of the sample prior to cooling can becompletely avoided, if so desired.

The device is suited for research laboratories in which for exampleseries of preforms of different composition are transformed intoamorphous alloys for series tests. Also the temperature and timeparameters can be varied from one sphere to the other by appropriatelyprogramming the process control. The invention is also adapted to themanufacture of platelet-shaped vitreous alloys on the industrial scale,insofar as the magazine 7 and the collecting recipient 9 are providedwith sufficiently great capacities.

We claim:
 1. A device for producing amorphous ceramic products or metalalloys by means of a high pressure autoclave in which firstly a preformof the sample is heated by means of laser beams up to meltingtemperature and then rapidly cooled down,below a process position (2),in which the sample is heated up and cooled down, an acoustinglevitation installation (12) is disposed, which is constituted by apiezoelectrically excited sound source and which levitates the sample inthe process position (2) without contacting it, characterized in thatthe process position (2) is disposed in the intersection point of atleast two laser beams (14, 15), which penetrate into the autoclave viawindows (19) in view of heating up the sample, two stamps (20, 21) aredisposed facing each other on either side of the process position (2) inthe autoclave (1), which are susceptible to be electromagneticallypushed towards each other, in order to crush the sample therebetween andthus rapidly cool it down.
 2. A device according to claim 1,characterized in that the process position (2) is situated in theintersection point of four laser beams, each of the laser beams runningalong the edge of an imagined four-sided pyramid.
 3. A device accordingto claim 2, characterized in that respectively two facing laser beamsare derived from a common laser generator (14 resp. 15).
 4. A deviceaccording to claim 1, characterized in that a multiwavelengths pyrometer(24) is directed onto the process position (2) through a window (25) inthe wall of the autoclave (1).
 5. A device according to claim 1,characterized in that a programmable process control unit is provided,which controls the laser generators, the levitation installation (12)and the stamps (20, 21).
 6. A device according to claim 1, characterizedin that an acoustically permeable catch basket is disposed between thelevitation installation (12) and the process position.